Process of making cellulose nitrate film and similar products



March 7, 1933. E, V DERHQEF 7 1,900,873

PROCESS OF MAKING CELLULOSE NITRATE FILM AND SIMILAR PRODUCTS Filed April 6, 1929 gwventoz,

Henry E. VanDerhoei Patented Mar. 7, 1933 UNITED STATES PATENT OFFICE HENRY E. VAN DERHOEE'OF BOCHESTER, NEW YORK, ASSIGNOR. '10 EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK PROCESS OF MAKING CELLULOSE NITRATE FILM AND SIMILAIt PRODUCTS Application flled April a,

This invention relates to nitrocellulose film and the like, and particularly to a process of producing such film.

Nitrocellulose film has been prepared heretofore by dissolving nitrocellulose in suitable solvents such as acetone together with plastifiers or softeners such as monochlornaphthalene. The dope thus prepared is a viscous material which is deposited in a thin layer upon a supporting surface, for example a revolving drum or wheel. As the drum or wheel revolves slowl the thin layer of dope is exposed to a1r and gradually hardens so that it can be stripped as a film which is subsequently dried. The process is relatively slow and the capacity of the apparatus employed is correspondingly reduced.

It is the object of the present invention to provide a process of producing flexible transparent nitrocellulose films rapidly and more economically with a minimum fire risk and maximum recovery of the solvents employed.

1 have discovered that nitrocellulose dopes may be hardened generally more rapidly and otherwise advantageously by exposing them to an atmosphere of steam or water vapor. This may be accomplished readily in a simple manner by disposing a layer of the dope on any suitable supporting surface. The dope may be placed then in a chamber or inclosure the atmosphere of which is supplied with steam or water vapor or with air which has been previously humidified. For commercial manufacture of film it is preferable to employ an apparatus in which a suitable surface, for example the surface of a rotating drum or wheel, is supplied continuously with the dope in the form of a thin layer. As the drum or wheel revolves, the layer of dope is carried through an atmosphere of steam or water vapor or of air previously humidified to the required degree. As the layer of dope advances through this atmosphere it coagulates or solidifies gradually but much more rapidly than in the practice heretofore emplo ed so that the film sooner reaches the con ition in which it may be strip ed from the surface, or, .in other words, t e drum or wheel may rotate more rapidly thus increasing the capacity of the 1929. Serial in. 353,049.

apparatus. When the film' has hardened sufficiently, it is stripped from the supporting surface and is delivered to a suitable drying compartment wherein it is subjected to further treatment to further dry the film before it is rolled on a reel or spool. The supporting surface is then preferably cleaned and again passes under the source of supply of the dope to receive the coating. The temperature to which the layer of dope is subjected may vary considerably.- The atmosphere containing steam or water vapor should be maintained at such a temperature as to prevent condensation and consequent wetting of the film or of the apparatus. Temperatures generally below 100 0. should be employed to prevent over-heating of the film, and I find that the most satisfactory temperature is approximately C. to 80 C.

As hereinbefore indicated, the procedure can be carried out in any suitable apparatus. I have, however, illustrated in the accompanying drawing an apparatus adapted for the practice of the invention, it being understood that this is merely illustrative. In the drawing the Figure l is a diagrammatic sectional view of a drum or cylinder with means for applying the coating of dope thereto.

Referring to the drawing, 1 indicates a V-shaped trough which is adapted to receive the dope. The lower part of this trough is provided with accurate edge-pieces 2 and 3, the latter being movable up and down by means of a screw 4, whereby the thickness of the film 5 is easily regulated. The edge-piece 2 projects slightly below the edge-piece 3, thus guiding the accurately shaped film of dope upon the polished cylindrical surface 7 of the wheel 8. This surface may be that described in the United States patent to Sulzer, Serial No. 1,466,733,'but any other suitable surface such as polished electrodeposited chromium may be used. The wheel 8 turns in the direction of the arrow, the sheet of dope on the surface 7 passing through a chamber 9. In this chamber, the film 5 of dope is still in a viscous condition and it can therefore settle under the influence of gravity sufficiently to permit the layer to equalize in thickness. If portions of the layer are relatively too thick and other portions of the layer are relatively too thin in spite of the accuracy of edgepieces 2 and 3, these inequalities will gradually work out in chamber 9 by settling of the thicker portions. The equalized film 5 is then carried forward by continued revolution of the wheel 8 and is subjected to the atmosphere maintained in the space between the wheel and the casing 10, which is substantially concentric with the surface of the wheel. This atmosphere, as hereinbefore indicated, consists of air and steam or water vapor. Preferably the air is pre-heated and humidified and is introduced to the casing 10 through an inlet pipe 11. After circulating around the wheel 8 it is withdrawn through an outlet 12 and carries with it the vapors of volatile solvents which separate from the film as it hardens on the Wheel. Suitable partitions 13 and 14 extend from the casing to a point closely adjacent to the film to prevent escape of the atmosphere except through the outlet as described.

At a point adjacent to the inlet pipe 11, the film which has now hardened sufficiently is stripped from the Wheel 8 and is withdrawn from the apparatus and guided over a roller 15 which directs it into the drying apparatus (not shown).

Between the point where the film is stripped from the surface of the wheel and the trough 1, I may provide any suitable cleaning or polishing apparatus such, for instance, as the one described in the United States patent to Reid, Serial No. 1,187,929. This apparatus includes a pipe 16 with fine perforations in its side through which water is supplied onto the surface-7. This pipe is perpendicular to the axis of the wheel 8. The cleanin liquid is not allowed to flow down the sur ace 7 to the stripped film but is taken up by a dam in the shape of a hollow roll 17 having its periphery covered with a layer of soft rubber 18 through which a series of fine apertures are provided communicating with the interior of the roll which is connected to a suction device so that the water is Withdrawn through the dam and out of the ap; paratus. The surface of the wheel may finely conditioned by'an absorbent 'roll 20 held against the surface by an adjustable spring 21.

In the apparatus as described the dope is supplied continuously to the wheel which in rotating carries the film through the atmosphere of steam or water vapor until it is sufficiently hardened so that it can be stripped and withdrawn. The dope in the trough may be maintained at above the room temperature so that the viscosity will be such as to permit the application of a coating of the desired thickness to the wheel. The temperature and moisture characteristics of the atmosphere may be regulated likewise to 1nsure rapid and effective hardening of the film,

the apparatus-being operative at speeds very materially exceeding those possible when air alone is employed.

The process as described is applicable to the treatment of cellulose nitrate dopes of varying composition. Many compositions of this kind have been developed and are in common use. The exact composition forms no part of the present invention but for purposes of illustration reference to a typical dope which can be utilized in preparing films in the manner described will be made. Preferably the nitrocellulose fibers are partially dehydrated with normal butyl alcohol as dis closed in the United States patent to Seel, No. 1,398,911. The mass of nitrocellulose fibers containing from 40% to 60% of butyl alcohol is dissolved in methyl alcohol as disclosed in the United States patent to Seel, Combs and Kemp, No. 1,380,258. The resulting dope may be supplied to the trough of the apparatus hereinbefore described, and, when treated therein in accordance with the invention, a film is formed which is suitable for photographic and other purposes. It retains some of the butyl alcohol which promotes better wearing qualities and increased flexibility.

My process may be applied for the preparation of films of thicknesses customarily employed in the photographic art, but thickor films or even thinner ones may be prepared in a condition of satisfactory transparency, flexibility and strength. The use of water vapor in hardening or setting such films not only increases the speed and consequent efiiciency of the operation but tends to counteract any tendency of the film to stick to the supporting surface so that very thin films can be roduced readily and rapidly b the procedure as described.

While the apparatus described herein affords a practicable means for preparing films, it is not an essential part of the invention and other apparatus or modifications of the apparatus described may be utilized. Various changes may be made moreover in the procedure,. the essential part of which is the utilization of steam or water vapor during the initial hardening of the dope to form a film. All such modifications are within the scope of the invention as hereinafter claimed.

Havin thus described my invention, what I c aim as new and desire to secure by Letters Patent is:

1. The process of manufacturing cellulose nitrate film which comprises simultaneously coagulating and curing a cellulose nitrate dope by subjecting it to an atmosphere of high relative humidity.

2. The process of manufacturing cellulose nitrate film which comprises simultaneously coagulating and curing a cellulose nitrate dope by subjecting it to an atmosphere containing water in the vapor phase.

' 35 day of 11%, 1929.

3. The process of manufacturing cellulose nitrate film which comprises simultaneously coagulating and curin a cellulose nitrate dope y subjecting it to the action of 5 steam. I

4. The process of manufacturing cellulose nitrate film having great length relative to width which comprises simultaneousl coagulating and curing a cellulose nitrate do e y subjecting it to an atmosphere of big relative humidity.

5. The process of producing a transparent cellulose nitrate film substantially free from residual solvent which comprises formin upon an appropriate surface a thin' layer 0 cellulose nitrate dope and thereafter simultaneously coagulating and curing said layer by subjecting it to the action of heated water vapor.

6. The process of producing a transparent cellulose nitrate film which com rises forming upon a smooth surface a t in layer of ce ulose nitrate dope and thereafter simultaneously coagulating and curing said layer bysubjecting it to the action of water vapor at a temperature not in excess of 100 C;

7. The process of producing a transparent cellulose nitrate film which com rises formin upon a smooth surface a t in layer of 3 cc lulose nitrate dope and thereafter simultaneously coagulating and curing said layer by subjecting it to the action of water vapor at a temperature of 6080 C.

Signed at Rochester, New York, this 2d NRY E. VAN DERHOEF. 

